SINGAPORE - Although Singapore has managed to reduce new infection cases to zero or just a few in the past few weeks, this does not mean that the country has successfully eliminated Covid-19 from the community, experts cautioned.
Complacency could set in if people start letting their guard down, in the belief that the country has triumphed over the virus.
Striking a cautionary note, Professor Teo Yik Ying, dean of the National University of Singapore's Saw Swee Hock School of Public Health, said Singapore will not be safe until the world is safe, as the presence of asymptomatic patients could still lead to community spread.
"From some of the global surveillance studies, we understand that more than half of the infected people are asymptomatic. So, unless we are able to screen everyone in Singapore, and to do so in a repeated manner, it will be unwise to proceed with the assumption that we have completely eliminated the virus in Singapore," Prof Teo said.
"We are still seeing a number of imported cases every day, and even if people are quarantined for 14 days, there could be the inevitable leakage if symptoms manifest after 14 days."
The true number of Covid-19 infections is also likely higher than the reported cases, said Associate Professor Alex Cook, an epidemiologist at the Saw Swee Hock School of Public Health.
"Take the case of someone who is infected, diagnosed and reported. But not everyone who is infected is diagnosed, and this could be because he is asymptomatic, or not going to a doctor when ill," he said.
"I am confident about Singapore's current testing capacity and that we are picking up lots of otherwise undetected cases, maybe as many as half of the true number of infections out there, but it is unrealistic to expect we (will) find them all."
Prof Cook said that having zero community cases should not be the target, even if it is laudable and "sounds like a good number", as it could breed a sense of complacency.
"The threat of Covid-19 will remain until we have mass vaccination," he warned.
With Singapore easing travel arrangements with other countries as well as gradually relaxing restrictions around social and recreational activities, interactions between people will increase, and infection importation risks will also edge higher, said Prof Teo.
When this happens, the need to retain precautionary measures such as mask wearing, strict personal hygiene and social distancing becomes even more critical, he added.
Professor Dale Fisher, a senior consultant at the division of infectious diseases at the National University Hospital, said that for the virus to be eradicated, one would generally have to look at two incubation periods, or 28 days in the case of Covid-19.
"However, even at that point, one would be reluctant to make the claim because of asymptomatic spread... and it is possible that there could be a few generations of asymptomatic spread, and then cases could appear," argued Prof Fisher.
He also pointed out that it could be tricky trying to estimate the proportion of asymptomatic cases, given the wide variation in estimated percentages and that people do have different thresholds before reporting symptoms.
Prof Fisher also noted that there is significant asymptomatic spread, with studies showing that the proportion of such cases could range from less than 10 per cent to around 90 per cent of all Covid-19 cases.
"I would say a reasonable estimate is about 40 per cent. Thus, it remains important to continue all infection prevention measures," he stressed.
"Zero cases is certainly nice, but I wouldn't support zero tolerance for cases. That would make the border restrictions harder to lift. I still think the aim should be to live with the virus while minimising case numbers. Selective nuanced border openings are important for every country to avoid more social and economic harm being done."